1. Field of the Invention
The present invention is generally concerned with semiconductor devices and specifically is concerned with a process for the passivation of semiconductor devices with amorphous silicon.
2. Description of the Prior Art
The purpose of applying a passivating film of an amorphous silicon to a semiconductor device is to ensure the uniformity of the current-voltage characteristic of the semiconductor device. With rectifiers and transistors, this is important, especially the current-voltage characteristic in the blocking direction, whereas, in the ease of thyristors, both the stability of the characteristic in the blocking direction and the stability of the characteristic in the forward (breakthrough) direction are important.
In prior art practice, a passivating film of amorphous silicon is vapor-deposited in vacuum, at least in the vicinity of the p-n junction.
Because of the linear spread of the vapor molecules when vapor-depositing in a high vacuum, a passivating film thickness is obtained which is a cosine function of the angle between the normal to the surface of the body of semiconductor material and the direction of the vapor beam. Thus, in order to obtain a relatively uniform coating on uneven surfaces and edges, the body of semiconductor material must be rotated around at least two axes with respect to the vapor stream during the vapor-deposition operation. Such rotation motion generally being obtained by means of a planetary gear system or the like.
The movement of the body of semiconductor material, during the vapor deposition operation, is also necessary in order to prevent the so-called shading effect which, arises during the build-up of the film. There also is a tendency for directional growth, columnar growth, and a material structure which is not completely dense. The latter, especially must be prevented where the film is to be used for passivation.
The present invention provides a process for depositing an amorphous silicon passivating film or layer on a body of semiconductor material. The layer or film has a uniform thickness, is fully dense, isotropic and stable.